The properties that impact the performance of semiconductor materials, for example, in solid state radiation detectors, include high resistivity, long carrier lifetimes and good carrier mobilities, low defects, and low carrier concentration (leading to high resistivity) when the material is not exposed to radiation. For gamma radiation, the most popularly used detectors are sodium-iodide (NaI) scintillators, high-purity germanium (HPGe) semiconductors and cadmium-zinc-telluride (CZT) semiconductors. For optimal resolution, HPGe detectors must be cooled to liquid nitrogen temperatures, limiting portability and ease of use. NaI detectors are operable at room temperatures but are significantly inferior to HPGe with respect to energy resolution. The most recent addition, CdZnTe, operates at room temperature, has improved resolution (compared to NaI), but has low hole mobility, reducing it to a single charge carrier detector. This is a well-known disadvantage that results in poor spectral performance, and reduced photopeak efficiency. This also limits the detector size to maintain reasonable resolution, as an event near the cathode will have different charge collection properties than an event near the anode.
Advancements in technology involving semiconductor production introduce the possibility that new materials may be considered for use in this field. For example, ultra-high vacuum molecular-beam-epitaxy (UHV-MBE) growth eliminates many of the contaminants that are problematic for bulk growth, and also enables precise control of layer thickness and dopant concentration. However, in many instances of epitaxial growth, lattice constant mismatch and thermal expansion coefficient mismatch between the semiconductor layer and the substrate on which it is grown result in the forming of defects, particularly in thin films. What is needed in the art, therefore, is an improved method that provides for semiconductor devices that overcome the challenges associated with those of conventional semiconductor devices.